Based on the synthetical analysis of lightning data and Doppler radar echoes from a strong convective system in Nanjing on 22 June 2006, relationship is found between lightning frequency and radar echo intensity. The Cloud-to-Ground (CG) flashes mainly occur in the echo intensity>40 dBz and high echo gradient region. In the different phases of the strong convective system development, the frequency of positive and negative CG flashes are various. Positive CG flashes occurred after convective system reached the mature stage. Positive CG lightning ratio increased remarkably. The greater lightning intensity is, the smaller flash frequency is. Apart from a few weak flash (|I| <10kA), their relationship basically is inverse phase.